Electrical signaling system.



R; H. MANSON. ELECTRICAL SIGNALING SYSTEM. APPLICATION FILED APR. 18,1907. 922,436. Patented May 18, 1909.

4 SHEETS-SHEET 1.

we b1 eases wk) 777m Stratum R. H. MANSON. ELECTRICAL SIGNALING SYSTEM.APPLICATION FILED APR. 18, 1907.

922,436. Patented 18, 1909.

4 S -SHEET 2.

ZWZ

W W 7770207 I a I g 1 =7 I W /5 snvanfo'c 4m lvil'ueboco V a U H70: mug

R. H. MANSON. ELECTRICAL SIGNALING SYSTEM. APPLICATION FILED APR. 18,1907.

922,436, Patented May 18, 1909.

4 BEEETs-BHEET 3.

linemen Wad/ZZZ? R. H. MANSON. ELECTRICAL SIGNALING SYSTEM.

APPLIOATIOTT FILED APR. 18, 1907.

Patented May 18, 1909.

4 SHEETS-SHEET 4.

ix" in case's UNITED STATES PATENT OFFICE."

RAY H. MANSON, OF ELYRIA, OHI O, ASSIGNOR TO THE DEAN ELECTRIC COMPANY,OF ELYRIA,

. OHIO, A CORPORATION OF OHIO.

Specification of Letters Patent.

Patented May 18, 1909.

Original application filed January 16,1906, Serial No. 296,309. Dividedand this application filed April 18, 1907.

' Serial No. 369,020.

To all whom it may concern;

Be it known that l, RAY l-I. MANsoN,a citizen of the United States,residing at Elyria,

.in the county of Lorain and State of Ohio,

have invented certain new and useful Improvements in ElectricalSignaling Systems, of which the following is a. specification,rcfcren'ce being had therein to the accompanying drawing.

My invention relates to electrical signaling systems, and has for itsobject the improve ment of such systems-and the apparatus used therein.

I t is especially designed for use in systems wherein a plurality ofsignals are to be manifested, or a plurality of signal devices are to beactuated over the same circuit; and in the form which- I shallhereinafter describe it finds a wide sphere of usefulness in thetelehone field. I contemplate applying it, however, to many otherclasses of systems, which need no special mention since the methods ofapplication will be sufficiently av parent after reading thedescription, to tl fose skilled in the electrical'arts.

For purposes of selective signaling, and as thebasis for the presentinvention, I employ periodic currents of different frequencies, and theprincipal merit of my design resides in the efficiency, economy andprecision oi.

production and application of such currents. At the present timestandard practice, and

particularly telephone engineering practice, s such as to render hneconstruction, as well as centra. oflice equipment, very expensive; and111 order to msure the largest possible returns from the heavyinvestments thus required, it is customary to serve a plurality ofstations over the same circuit wherever possible. In order to renderthis class of service satisfactory it is demanded thatfeach station maycall and may itself initiate calls, with out disturbing or alarming theother stations on the same circuit. This may be accomplished in avariety of ways, but where the number of stations comparatively small,

the best way is by means of harmonic signaling, in which the receivingdevices at the several stations are arranged so that each will respondonly ten definite and predetermined kind ofcurrent. Such systems havebeen designed and extensively used in telephone work, having fourdistinctive currents generated at the central ofiice, and all the substation ringers tuned to respond to one or another of these currents,only. The necessary equipment, however, has heretofore been expensiveboth in first cost and inits subsequent, maintenance and operation. Manysmali' exchanges have thus been prevented from instaling standardparty-line equi ments, because of their prohibitive cost. uch equipmentshave heretofore'included special generators, having four differentwindings or four different armatures, each adapted to produce current ofa particular frequency; and since the frequency of a periodic currentvaries with the speed of the machine generating it, these machines havenot only been fitted with devices for maintaining their speed constant,but it has been necessary to keep them running all the time, for theobvious reason that they couldnot be started and broughtu pto full speedso as to deliver the proper current for each call to be made. As themachines have usually been run by means of electric motors, and as theidle or friction load in running is considerable, the total currentconsumption has been a factor to consider, even in large exchanges.

According to my present invention I provide a plurality ofpole-changers, each With its own motor, preferably governed by anindividual relay, the working parts of each pole-changer being tuned soas to have a distinctive period, which -determines the frequency of thecurrent output, and which is constant under all circumstances, whethercontinuously running or freshly started. I associate with thesepolc-changers'an equal number of transformers, each especially adaptedto the particular frequency of current with which it is to be used, andalso a number of condensers which may likewise be suitably proportionedto the several currents. The motors for the pole-changers, which areconveniently electro-magnetic vibrators, may be run constantly by meansof closed circuit primary batteries, such as the well known gravitybatteries, and the pole-changing contacts may be supplied from separateopencircuit batteries; but I preferably arrange both the motors and thecontacts to be supplied from a common source, and controlled as to theirsupply by the individual relays. This enables me to connect my entiresystem to a common source, such as, for example, i

the main storage battery of an exchange.

' having a veryvlow internal resistance,

, current flow through my machines is depend- .dinary power-drivengenerator.

ent entirely upon the internal conditions in the machines themselves,and theycan thus be designed for any given voltage and current outputwith the same precision as an or- An incidental advantage in the use ofseparate motors for these machines lies in this,-that each machine willcontinue to operate perfectly, even though one or machines in the sameset may be disabled.

This is not so with the generating sets heretofore employed, and it hasalways been considered necessary to have these sets installed induplicate, since the breaking down of the ringing machine wouldobviously cripple all the work of an exchange. In the present case itis'o'nly necessary to carry a small stock ofparts in order to be able toremedy any tem orary break-down almost instantly,

. and I makethe units composing each set interchangeable,- so that incase of the complete destruction of one unit, another may besubstituted, and properly tuned, with little trouble and no delay.Another great advantage in the use of separate motors lies in thepossibility thus afforded for wide scope in choice of fre uencies to beused. In rotary or other madliines heretofore employed, because of thecommon moving arts, frequencies have had to be taken w ich weresubstantially multiples ofeach other, as 33, 66, 50, and 100 cycles.With separate motors, I am enabled on the contrary, to choose anyfrequencies I wish; and I find it'best to avoid common multiples,because of their well understood liability to interfere.

I mount my ole-changing set, with its transformers an which forms acomplete portable unit in itself, and which preferably has provisionalso for containing primary or secondary battery cells to run themachines, if desired.

In order to protect my machines, and also the operators ringin leads,from excessive current due to groun s or short circuits upon the lines,I introduce into each lead a suitable compensatin resistance, shape ofan e ectro-magnet1c vibrator havin only a few turns of large wire, sothat it w' not respond to the ordinary ringing currents,

but upon an undue rise in current will commence to vibrate, therebyintroducing a resistance proportional to the current flow.

The present application is a division of my earlier apphcation filedJanuary 16, 1906,

Serial No. 296,309.

My invention is illustrated, as to oneemof generating a very large moreof the other.

condensers, in a cabinet preferably in the bodiment, in the accompanyingdrawings, in which'- Figure 1 is a front view of a cabinet with thecover and face panel removed, showing the pole-changing units upon itsto and the transformers and condensers wit in it; Fig. 2 is a lan viewof one of the polechanging units; Figs. 3 and 4 are, respectively, aside view and a face view of the same unit, the base being shown in Fig.3 in section; Fig, 5 is a diagram of the circuits of my rin ing outfitas applied to a standard common attery manna exchange equipment.

Referring first to Fig. 1, A is a cabinet, which I have shown with apaneled back a, sides a, a base (1 and a fiat top (1 Within this cabinetand across the two sides u,a I mount a shelf a, of suificient weight andstrength to carry the transformers T T T T and the condensers O. Thelatter are assembled together f0l' CO11V8I1iGI1C6 lI1 handling, in aseparate box or cabinet a in which the distance pieces a, are fitted,and from end to end of which a bar 0. extends, so that the condensersare securely held against displacement. The front of my cabinet A isclosed when it is in use by means of a removable panel or door, notshown. Upon the top a is secured a thick rectangular base of felt orsimilar sound insulator f. Upon this rests the base F, which. is commonto all of the pole-changers. Each pole-changer comprises the apparatusshown in Figs. 2, 3 and 4, mounted upon aseparate base F, secured tosolid posts f f f f and f These posts, as well as the common base F, maybe of woodor similar material, and are made sufficiently reliablefoundation for the support and alinement of the pole-changers. The basesof the latter are raised up on the posts f -f 2.

etc., in order to leave a clear space beneath them for the pendulums ortuning weights.

Each base F may also be insulated from its supports f 2 "etc., as shownat f*, if desired. It will be observed that the individual basesthemselves are heavy and substantial, and as they are of slate material,and all of the parts are insulated, the sound produced by the outfit inringing is not suflicientlyloud to be objectionable, which has been thecase heretofore with many pieces of apparatus of this character.

The transformers T T T and T in point of their general design form nopart of the present invention; but they have one or two special featureswhich I have found necessary in order to adapt them to my purposes. Itwill be observed that the iron core t of transformer T is much largerthan the core t of the transformer T, and this in turn is larger thanthe core t of the transformer T while the core t smallest; of all. Thereis a corresponding or similar of transformer T is the difference in thewindings of these transformers. The transformer T is used with currentsof the lowest frequency, and in winding; T is used with the next higher'frequency, its iron circuit being therefore further reduced, and itswinding changed; and T is used for the highest frequency,having'therefore a comparatively small amount of iron in its magneticcircuit, and its winding so proportioned as to produce the necessary lowco-efficient of self-induction. It is unnecessary for me to give theformulae for these transformers, the same being well .known toengineers, and I will merely call attention to the characteristicproportions of each transformer, by which, in conjunction with theproper design of the pole-changers and if necessary of the condensers, Imaintain approximately uniform conditions for ringing currents of allfrequencies.

Referring now more particularly to Figs. 2, 3 and 4, wherein one of thepole-changing units is shown on a larger scale, F, as before noted, is aheavy base of slate or other suitable material, upon which is erectedthe yoke frame F, carrying a pair of magnetic cores f with windings f.The forward ends of these magnetic cores pass through and are secured toa second vertical yoke frame F, which is itself secured to the base byone or more screw-bolts f 9 passing up from beneath, and carrying tailedwashers f or other means for attaching circuit wires. It will be notedfrom the diagram that one side .of each pair of contacts is to battery,and I referably make these battery connections t rough the frame, thussimplifying the wiring very materially. Upon the upper end of the frameF a heavy transverse block F is secured, u on which the stiff spring Sis held by the clamping plate F preferably seated in a depression orcross groove milled. out in the heavier block. I make these parts heavyand solid for a double purpose,first, in

- order to have the fastenings absolutely secure, and, second, toprevent the communication of vibrations through the parts of themachine. The spring S carries the armature F and the contact member Fwhich are riveted together at f through the body of the spring, and uponopposite faces thereof. The contact member is bent out at right anglesfrom the plane of the armature, and upon its outer end, which is againreturned at a right angle, I fastenthe contact spring In order that thismay yield on the back stroke when it touches the twin contact f, but maybe rigid when the armature is drawn forward, I rovide a stiff backingmember f which is lield at its upper end to the spring and also upon thecontact member F by 'means of the screws j. The armature F normallyhangs vertically directly in front of the poles of the magnets f which Imaymake adjustable with regard to the frame I by means of the nuts fAttached 'to the armature and depending therefrom is the rod f carryingthe tuning weight or pendulum f The back contact forthis vibratorymechanism is preferab y the platinum point of a thumb SCIGW having amilled head by means of which it may be adjusted in the post f securedupon a base piece f and provided with a set screw f, by which thecontact screw may be locked. All of the contact posts in my device havesplit heads and set screws for this same purpose. Circuit connections tothe post are effected through the tailed washer 1 attached beneath t ebase to the screw bolt f. The plate f is employed, with its two screwbolts through the base, in order to prevent any possible turning of thepost j, and conse uent disarrangement of the contact f. T e post isrigidly set in the plate by means of solder or a steady pin or a squaredshoulder let into the plate. A solid construction is thus attained whichwill not-he disturbed by the continuous vibration of the'contacts.

The parts of the apparatus thus described constitute the motor mechanismof the individual or unit pole-changer. The electromagnets f areconnected on one side to the posts f and on the other side to ground,the armature and frame bein to battery when the circuit is closed. In tiis condition the armature will'be vibrated, and by properly adjustingthe screw contart f, this vibration may be rendered uniform and smooth,and its frequency determined to a certainty by means of the pendulum bobor weight f. The pole-changing means operated by this motor devicecomprise a pair of transverse springs pp, the first of which is inmetallic contact with the parts of the armature and frame, and so tobattery, while the second is to ground through a flexible spring ppassing upward through the central opening in'the member F and kept fromtouching the latter by means of an insulating bushing p These springsare stiffened by metallic backing strips pprecisely similar to thestrips j, and for t e same purpose, that is, each spring p or p is quiteflexible, but the backing strips are relatively stiff, hence-the springsare permitted to give in one direction, but not in the other. It willappear that the opposite ends of the springs must give in oppositedirections, hence the strips pp are on the outside faces on one side,and upon the inside faces on the other (see particularly Fig. 2). Forconvenienre of mounting, I assemble the split head post, wit a setscrew, similar to e post f and screws f All four contacts may thereforebe adjusted with great accuracy, and held positively thereafter. Theposts p p carrying the screws pi-flf, are mounted upon opposite .ends ofa plate 1), and the posts p 'p are mounted upon a similar plate Thesetwo plates are secured to the base by means of screw bolts, in a similarmanner to the plate If. They are connected to suitable termina s mountedon the base, and thence to opposite sides of the primary winding of oneof the transformers T. Since the two springs 'p-p' are connectedrespectively to battery and to ground, and as the contacts are adjustedso that one of the s rings will make on one side and break on t e otherside, at the same time that the other spring breaks on the first sideand makes on the other, and vice versa, it will be apparent that as thearmature vibrates the springs back and forth between the-contacts,battery and ground will be rapidly, simultaneously and alternatelyconnected to the two plates p p For the purpose of securing the sprin sp in an eflicient manner, I mount .aru ber block p on the top of'theblock F, and secure the spring u on tile nubber. It is neces sary toprovide t orougii insulation between these sprin s and the other parts,since the potential iiference between them represents the full strengthof the battery or other source of supply, and also since a ground uponthe live side of the battery would not only produce disastrous resultsin the individual unit, but would temporarily disarrange other portionsof the exchange mechanism.

Having thus described the individual unit I will revert again to Fig. 1.I have referred to the pendulum bob or weight f as determining the pitchor tune of the individual unit. In Fig. 1 the four units, designated asP P P and P are fitted with weights of different sizes and masses. Theymay also be difierently adjusted upon the rods f. The preferable methodby which I effect this tuning is to take the armature with its movingparts assembled upon it, and put it in a standard frame where it isexposed to magnetic effects produced by current of the frequency towhich it is intended to respond. A weight exactly corresponding to thatcord to the calling subscriber.

which is to be used upon it is then adjusted upon the rod until theproper point is deter mined at which the greatest efficiency isattained, and a mark is made upon the rod to indicate this oint. Thetest weight is then 'removed, an the final or working weight is drivenupon the rod up to the point marked. This method of tunin ables me 'toproduce a solutely uniform results, with considerable economy inmanufacture.

Turning now to the circuit shown in Fig. 5, L L represent pairs ofconnectin plugs adapted for use with a manual switc board of standarddesign, each pair of plugs being connected by cord conductors 1, 2, 3and 4, with interposed-condensers, and bridged relays controlling suervisory signals m, all of standard type an arrangement. The line jacksandline circuits with which these plugs cooperate are not shown in thediagram, be: ing perfectly familiar to all engineers. They may be of anysuitable or desired construction and arrangement, it being presupposedfor the purposes of this invention, however, that the line circuits aretwo-wire or metallic circuits, and each with one or more sub-stationringers connected across its component wires.

My generating set will work upon ground ed circuits, and in fact I haveshown the secondaries of the transformers all grounded on one side, but,as a general rule, and in accordance with modern practice, these groundsare common, and the current is brought back from the sub-stations to thecentral office and passes to ground at the ringing keys.

and assembling en- Associated with each plug L is a selective be closedby means of a suitable lever or button, in the usual manner.Associated'with these pairs are other pairs 7c 7c -7c and 7c,simultaneously controlled. Associated with all of these selectivecontacts is a pair of springs k which normally rest upon contactsthrough which the cord circuit is completed, but are separated therefromwhen any one of the selective buttons is in use, so that when anyringing current is put on the plug L it will be prevented from flowingback over the The contacts k,-7c 7c and k are connected by means ofwires 5, 6, 7 and 8 to the leads 12, 11, 10 and 9, which pass to therelays R R,

R and R of the pole-changers P P P and the contacts 70, k k and 7c areconnected together and to ground, and when the spring 7:

transformers T T T and T, associated,

is actuated it grounds the sleeve of the plug L, while it opens the cordon the other side. The springs k is, k and k are connected by W1I3S14,15,16 and 17 to the leads 21,20,19, 18, which pass through contactsof the compensating vibrators V V V and V, to the secondary windings t,vt t and t of the with the pole-changers P P P and P. The primarywinding of each of these transformers is connected on one side by wire22 to the inside contacts of the pole-changer,

and on the other side by wire 23 to the out-' side or alternate contactsof the pole-changer. Across these two wires is bridged a condenser C,which takes up the discharges from the coil and prevents sparking atthe'contacts, besides rendering the effect in the winding more uniformand efiicient.

The battery wire 13 is connected to the armatures r 1" r and 1"? of therelays R, R, R R and thence in each case when these relays are energizedby the wire'24 to the armature structure F and the contact spring fsecured thereto, also tothe pole-changing spring 10. The oppositepole-changing spring 3) is grounded. The motor magnet f 8 is connectedbetween the ground and the contact f -by wire 25, and across thecontacts f 12 and f is bridged a condenser C for the purpose of takin upthe extra current and preventing sparking.

The operation of my s stem thus described is as follows: The p ugs L Lhaving been inserted in order to efl'ect a connection, and the operatorbeing apprised of the party wanted on the line with which connection hasbeen made, she presses down the appropriate button which we will assumeto be Z, and at the same time spreads apart the springs 7c. A circuit isat once established -through contacts k as follows: battery B,

13, R, 9',- 8, k and ground back to battery. The relay R thereuponbecomes energized and pulls up its armature 7', closing the operatincircuit of the motor magnet f of the num .r one pole-changer P, asfollows: B, 13, r, 24, F f f 25, f", and ground back to battery. Thearmature F is thereupon pulled up, breaking apart the contacts f, f,then released to close said contacts, and so on continuously vibratingat a definite pitch predetermined by the mass and adjustment of thependulum f This vibration of the armature causes the springs 12, p toplay back andforth between their contacts, and so to alternately connectbattery and ground on each wire 22 and 23, so as to produce rapidreversals of ourrent in the pri- 'mary wlnding t of the transformer .T.The operation of the key is has connected the secondary of thistransformer to the tip of the lug L by the following path: If", 18, V,17, 8 and tip of plug L. From the tip of the plug this circuit iscompleted out over the line with which the plug istemporarilyassociated, through the one or more ringers upon that line,and if the circuit is metallic back to the central office and throughthesleeve of the lug to the key It to ground; or

if the circuit is a single wire circuit, then to its associatedtransformer has the most iron and the greatest number of turns in itswinding, hence the signal current that is generated in the secondary 0fthe transformer and sent to line, is of a low frequency determined-bythe adjustment of the constants to which I have referred. Theseconstants in the case of each. transformer and its pole-changer are soadjusted, however, that the'amount of energy sent to line will be fairlyuniform in all cases. i

The operation of the other selective keys and of the other'pole-changersis substantially the same, except as regards the frequencies. Thecompensating vibrators V V, etc., are included to complete the lay-out,and not in themselves as parts of the present invention, although incooperation with the apparatus described they form a very advantageousmeans for automatically increasing the resistance of the circuit upon anexcessive current flow therein, and, moreover, this increase ispractically proportionate to such increase in current.

From the foregoing description and statement of operation it will now beapparent that I effect the greatest economies, and attain the highestefficiency, combined with perfect precision in operation. There isnothing more accurate and more uniform in its action than a properlytuned reed or pendulum. There is no periodic vibrator which can bebrought into full operation with a smaller time-loss, and it is to beparticularly noted that this is very important, because'if the ordinaryrotary generator be started u in making a call, the rate of alternationwill be accelerated as the machine speeds up, from zero to maximum, andas a result all the ringers on the line will be operated in succession.In my case action is so uick as to have no effect whatever on any ut theone ringer which it is designed to actuate. The very important featurein this circuit is the inclusion of the; controlling relays R R incircuit with the ringing keys, whereby I am enabled to maintain theoperating current in purely local circuits, and prevent any possibletrouble in the keys from that source. The ringing currents, of course,pass through the keys, but the relays may be so wound as to take verylittle current, and alsoso the will ofl er very high impedance. Thus itwill be seen that the current flow through the op erators key, closingthe actuating circuit of the pole changer, is limited by the resistanceof the relay coils contained in this circuit,

such coils being preferably of high resistance, and this circuit isindependent of the c1rcu1t through the pole changer 'and transformerstitute a means for limiting the current flow through the actuating keyindependent of the current flow through the pole changer P and winding tThe relay coils also maintain a constant current flow through theactuating key for varying currents through the pole changer andtransformer winding.

I am aware that it has been propose fore to use vibrating reeds ortongues W1 h pole-changing contacts, for roducing alternating current. Ibelieve, owever, that I am the first to produce a system such as that Ihave described, wherein currents of different frequencies, andapproximating in character to those of the standard ringing generators,may be produced from pole-changers with precision, and so as to operatewith high efficiency. By combining transformers With my pole-changers,as shown, I am enabled not only to approximate the characteristics ofordinary generator current'in the ringing leads, but also to raise andregulate the voltage perfectly while workin if desired, on a source oflow potentiaI. As I have before pointed out, it is possible to connec'tthis system directly on the main storage battery of any common batteryexchange, and this I believehas never been accomplished before, hence Ifeel entitled to claim the combination I have thus made available, inbroad terms.

Many changes may be made in details of construction and in the circuitconnections without de arting from the spirit of my invention. t is notlimited to any particular type of connective or linecircuits, nor evento telephone circuits as such; and I desire my claims to be broadlyconstrued so as to cover all non-essential variations.

Having thus described my invention, what I claim-and desire to secure byLetters Patent 1s 1. In a signaling system, a source of electric energy,a pole changer adapted to be connected thereto, a transformer having oneofits windings connected to such pole changer and a second windingconnected to signaling leads, a key for actuating such pole changer andmeans for limiting the flow of current through such key independent ofthe current flowing through such pole changer.

2. In a signaling system, a source of electric energy, a pole changeradapted to be connected thereto, a transformer having one of itswindings connected to such pole changer which closes a circuit throughand a second winding connected to signaling leads, a key for actuatingsuch pole changer and means for maintaining a constant currents throughsuch pole changer.

3. In a signaling system, a source of electric energy, a pole changeradapted to be conrent flow through such key for varying curnectedthereto, a transformer having one of its windings connected to such olechanger and a second winding connecte to signaling leads, a key'foractuating such pole changer and means formaintaining a comparativelyleads, a key for actuating such pole changer and means for maintainingsuch .key in a local circuit independent of the circuits through suchpole changer and transformer.

5. In a signaling system, a source of electric energy, a pole changeradapted to be connected thereto, a transformerhaving one of its windingsconnected to such pole changer and a second winding connected tosignaling leads, a key for actuating such pole changer, a relay adaptedto be operated by the closing of such key and contacts carried by suchrelay for controlling the operating circuit of .such pole changer.

6. In a signaling system, a source of electric energy, va pole changeradapted to be connected thereto, atransformcr having one of. itswindings connected to such pole changer and a second winding connectedto signaling leads, a key for actuating such pole changer, means formaintaining such key in a local circuit independent of the circuitsthrough such pole changer and transformer and a second key located insuch signaling circuit for con-- trolling the same.

7. In a signaling system, a source of electric energy, a pole changeradapted to be connected thereto, a transformer having one of itswindings connected to such pole changer and a second winding connectedto signaling leads, a key for actuating such pole changer, means formaintaining such key in a local circuit independent of the circuitsthrough such pole changer and transformer, a i

second ke located in such signaling circuit for contro ling the same andmeans for simultaneously operating such keys.

8. In a signaling system, a source of electric energy, a pole changeradapted to be connected thereto, a transformer having one of itswindings connected to such pole changer and a second winding connectedto signaling leads, a key for actuating such pole changer, means formaintaining a constant current fio w through such key for varyingcurrents through such pole changer and a second ke located in suchsignaling circuit for controlling the same.

9. In a signaling system, a source of electric energy, a pole changeradapted to be connected thereto, a transformer having one of itswindings connected to suchpole changer and a second winding connected tosignaling leads, a key for actuating such pole changer, means formaintaining a constant current flow through such key for varyingcurrents through such pole changer, a second key located in suchsignaling circuit for controlling the same and means for simultaneouslyoperating such keys.

10. In a singaling s stem, a source of electric energy, a plurality ofdiversely tuned pole changers adapted to be connected thereto, aplurality of transfomers having primary windings connected to such polechangers and secondary windings connected to common signaling leads,tuned signaling devices in circuit with such leads, a key for actuatinga desired one of such pole changers and thereby causing current flow ofdefinite frequency in such signaling circuit and the operation of thecorresponding signaling device and no other and means for maintainingsuch key in a local circuit independent of the circuits through suchpole changer and transformer.

1 1. In a signaling system, a source of electric energy, a plurality ofdiversely'tuned pole changers adapted to be connected thereto, aplurality of transformers having primary windings connected to such polechangers and secondary windings connected to common signaling leads,tuned signaling devices in circuit with such leads, a key for actuatinga desired one of such pole changers and thereby causing current flow ofdefinite frequency in such signaling circuit and the operation of thecorresponding signaling device and no other, means for maintaining suchkey in a local circuit independent of the circuits through such 'polechanger and transformer, and a second key located in such signalingcircuit for controlling the same.

12. In a signaling system, a source of electric energy, a plurality ofdiversely tuned pole changers adapted to be connected thereto, aplurality of transformers having primary windings connected to such polechangers and secondary windings connected to common signaling leads,tuned signaling devices in circuit with such leads, a key for actuatinga desired one of such pole changers and thereby causing current flow ofdefinite frequency in such signaling circuit and the operation of thecorresponding signaling device and no other, a relay adapted to beoperated by such keyand contacts carried by such relay for controllingthe operating circuit of the pole changer.

13. In. a signaling system, a source of electric energy, a plurality ofdiversely tuned pole changers adapted to be connected thereto, aplurality of transformers having primary windings connected to such polechangers and secondary windings connected to common signaling leads,tuned signaling devices in circuit with such leads, a key for actuatinga desired one of such pole changers and thereby causing current flow ofdefinite frequency in such signaling circuit and the operation of thecorresponding signaling device and no other, a relay adapted to beoperated by such key and contacts carried by such relay for controllingthe operating circuit of such pole changer, a second key located in suchsignaling circuit for controlling the same and means for simultaneouslyoperating such keys.

In testimony whereof I aifix my signature in presence of two witnesses.

RAY H. MANSON.

'W'itncsses.

S. J. RonEnTs, S. P. KINGSTON.

